Plastic radiation and acoustic barrier compositions containing a thixotropic agent



United States Patent f US. Cl. 25247 18 Claims ABSTRACT OF THEDISCLOSURE A composition comprising a hardenable or thermoset resin, athixotropic agent and a radiation attenuator; the hardened or curedproduct thereof; methods of applying this composition in a thixotropicstate in the manner of plaster and hardening or curing it to yieldstructures shielded against noise and/or penetrating radiation,particularly in seamless applications.

This application is a contin-uation-in-part of my application S.N.550,596, filed May 17, 1966, now abandoned, entitled Plastic Radiationand Acoustic Barriers.

This invention relates to new and improved plastic radiation andacoustic barrier compositions. More particularly, it relates tothixotropic plastic radiation and acoustic barrier compositions whichmay be applied by troweling or spraying to vertical surfaces withoutsagging or running.

These compositions comprise a hardenable or thermo set resin, athixotropic agent and a radiation attenuator; hardened or cured productsthereof; methods of applying these compositions in a thixotropic state,followed by subsequent hardening or curing; and structures shieldedagainst noise and penetrating radiation by such applications,particularly in seamless applications.

It is well known to utilize dispersions of various heavy metals inplastics for radiation shielding purposes. Such compositions are,however, fluid and hence it has been necessary to use molds wherein theycould be solidified by heat, pressure or curing reactions of varioustypes. Their final emplacement has accordingly been in solid form andfrequently makes use of nails, screws or other mechanical fasteningmethods.

The fluidity of these compositions has prevented their directapplication to vertical surfaces which enclose sources of radiant oracoustic energy. Running and sagging of such compositions isparticularly severe because of their necessarily high density whichfrequently reaches 6.5 g./cc. or more. Moreover, the shielding weightsrequired for even moderately powerful sources are substantial. TypicalX-ray machines operating in the usual 100-150 kvp. range requireshielding of at least 4 lbs. of lead per square foot of wall area. Morepowerful installations, particularly those making use of radioisotopes,require several times that amount of shielding. The preparation ofshielding compositions which are sufliciently plastic to permit readyapplication but which, once applied, are able to sustain their ownWeight of 4 lbs/sq. ft. or more until hardening by some mechanism hasset in, has not been possible heretofore.

Accordingly it has been standard practice to provide shielding by usinglead or other radiation absorbing materials in rigid geometric shapessuch as sheet or block. Such shapes are frequently incorporated into orbonded onto conventional building materials, ie plywood, concrete block,lath, etc. Use of such discontinuous shielding is subject to leakage atjoints and fastenings and a variety of methods have been developed tominimize such leak- 3,438,903 Patented Apr. 15, 1969 age. Among theseare overlapping lead sheets, staggering of blocks, lead-headed nails andlead-containing mortar. Nevertheless, experience shows that theinstallation in a typical X-ray room of many hundreds of individualshielding units, each surrounded by a seam or joint, does result inleakage at specific points. Such leakage may readily be determined bysurveying the exterior walls of such rooms while penetrating radiationstrikes the interior walls. Further, discontinuities in the walls suchas electric switches, conduit or pipe present particularly difiicultshielding problems and are frequent sources of leakage. By contrast, thecompositions of the present invention provide a completely seamless,imperforate barrier which, upon survey, is found to be free fromleakage.

Accordingly it is an object of this invention to provide a radiation oracoustic barrier which may be applied to walls of ordinary constructionby troweling or spraying without sagging or running. It is a furtherobject of this invention to provide completely seamless and imperforateradiation and acoustic barriers. It is still a further object of thisinvention to provide radiation and acoustic barriers which offercomplete design freedom with respect to size, curvature and shape.Finally it is yet another object of this invention to provide radiationand acoustic barriers which adhere strongly to a wide variety ofsubstrates, e.g. concrete, wood, metal, ceramic, glass, plaster, etc.Other objects, features and advantages of this invention will becomeapparent from the following description and appended claims.

According to the present invention, I achieve these objects byindurating plastic radiation and acoustic barrier compositionscomprising a hardenable or thermoset resin, its hardener or curing agentand a radiation attenuator, by the incorporation therein of athixotropic agent. Surprisingly, such thixotropic compositions, whenformulated in accordance with the present invention, are suflicientlyplastic to permit application by troweling or spraying and yet will notsag or run from vertical surfaces. Even more surprisingly, thecompositions of the present invention are able to sustain themselves onvertical surfaces at Weights of even 16 lbs. or more per square foot ofwall area.

Thus, the compositions I have devised comprise a hardenable or thermosetresin, a thixotropic agent and a radiation attenuator which can beformulated into thixotropic compositions having, for example, theconsistency of plaster or cement, and are capable of being applied tostructures including vertical surfaces without sagging to the desiredthickness in seamless, imperforate layers by employing the conventionaltechniques which are presently employed in the building trades such asby troweling or spraying, etc. and allowing the applied formulation toharden or cure, for example at ambient temperatures.

The use of such formulations allows complete architectural freedom. Forexample, a building or other structure can be designed without regardfor radiation or accoustical requirements, in any size, curvature orshape, or of substantially any material, and all or any portion thereofcan be rendered radiation or acoustic proof by applying the compositionsof this invention. Thus, a hospital or clinic can be designed and builtwithout regard to radiation problems. Thereafter any portion thereof canbe converted, for example, to an X-ray laboratory by merely applyingthese compositions to selected areas thereof to the desired thickness inthe manner of plaster to yield a seamless and imperforate radiationbarrier.

Thixotropic agents have the property, when dispersed in suitable media,of exhibiting a variable viscosity which depends on the shear stressapplied to the dispersion. At low shear stresses such thixotropicdispersions have high viscosities while at high shear stresses they havelow viscosities. This phenomenon is believed to be due to the formationof a gel structure at low shear stresses and its progressive disruptionas shear stresses increase. While this behavior is known and utilized,for example in paints and resin gel coats, the demands placed upon thethixotropic agent in the barrier compositions of the present inventionfar exceed those of all previous applications. On the one hand, thepresent barrier compositions contain high loadings of radiationattenuator which, with the additional viscosity developed by thethixotropic agent, would have been thought to preclude application bytroweling or spraying. On the other hand, the extremely high density ofthese new compositions, coupled with the required thickness of up to /2inch or more, would have been thought to preclude the development by thethixotropic agent of sufficient gel structure to prevent running orsagging from vertical surfaces.

Thixotropic agents vary widely in effectiveness as do the requirementsof the various polymeric systems contemplated in this invention. Systemswith viscous resins and high attenuator loadings will require lessthixotropic agent than systems with more fluid resins and low attenuatorloadings. Generally the objects of this invention are met by thixotropeconcentrations from about 0.2% to about 7.5%, and in preferredcompositions by about 0.2% to 2.5% by weight. Typical thixotropic agentsand their approximate preferred concentrations by weight in the barriercompositions of the present invention are as follows: Colloidal silica,0.21.0%; hydrogenated castor oil, OJ-1.5%; bentonite or kaolinite clays,2.5-7.5% or more; carboxyl vinyl polymers such as those marketed by theB. F. Goodrich Chemical Company of Cleveland, Ohio, under the tradenamesCarbopol and Carboset, 0.5-5.0%; organo-metallic complexes such as thosemarketed by the Lubrizol Corporation of Cleveland, Ohio, under thetra'dename Ircogel, 1.5-7.5 Colloidal cellulose such as those marketedunder the trademark Avicel; colloidal asbestos such as those marketedunder the trademark Avibest, by American Viscose Company. The action ofcolloidal silica may be further reinforced by the addition of aboutODS-0.5% of a polyol such as ethylene glycol, glycerol, or a higheranalogue.

Thixotropes are generally most effective when their distribution in theresin phase is such that their ultimate particle size is attained. Thisultimate distribution is achieved by mixing under high shear conditionssuch as provided, for example, by the Cowles Dissolver or Dispersonic.Various other means of reducing the thixotropic agent to its ultimateparticle size, including particularly grinding and ultrasonic action,may also be utilized. Although lead is the preferred powdered radiationattenuator, other metals of high atomic number and high density, as wellas their compounds, salts and mixtures or alloys, may be used in thepresent invention. Among the powdered radiation attenuators which can beused are, beside lead, the metals wolfram, bismuth, tantalum, thallium,uranium, gold, silver, iron and the compounds ferrophosphorus, leadsulfate, lead chromate, lead oxide, lead hydroxide, lead sulfide and thecorresponding compounds of the other above-named metals. Other useableradiation attenuators will be readily apparent to those skilled in theart.

It will be understood that according to the method of application andintended use of the present radiation and acoustic barriers the size ofthe attenuator particles may vary considerably. For barriers where roughsurfaces are acceptable or desirable particle sizes of about 80 mesh orcoarser may be used. For smoother coatings smaller attenuator particles,to about 400 mesh or less, are preferred. A controlled range of particlesizes will permit a closer packing within the resin matrix since thefiner particles will fit into the interstices left by the largerparticles. Barrier compositions comprised of such multiple particlesizesare therefore especially effective.

A major factor in the effectiveness and applicability of the new plasticshielding compositions is the proportion of attenuator containedtherein. A high proportion of attenuator results in a very effectivebarrier which will, however, respond poorly to troweling or spraying.Conversely, a low proportion of attenuator provides a less effectivebarrier but enhanced applicability. While the new radiation and acousticbarriers can be formulated with any attenuator concentration up to andeven above about 9 8% by weight, high barrier values combined withexcellent application characteristics are obtained with attenuatorconcentrations from about 75% to about by weight.

The attenuator particles are bound into a cohesive whole by the resin.It is apparent that the adhesive characteristics of the resin, withrespect to both the attenuator particles and the substrate to which thecomposition is to be applied, are an important consideration. The sameis true of the mechanical properties of the resin. The new radiation andacoustic barriers can be formulated with hardenable or thermoset resinssuch as epoxy, unsaturated polyester or polyurethane resin, each incombination with a suitable hardener or curing agent. Other suitablehardenable or thermoset resins may also be employed. The resin generallycomprises less than about 25% by weight of the new barrier compositionsand in preferred formulations comprises from about 1.5% to about 20% byweight.

The function of the hardener or curing agent is to cure the hardenableor thermoset resin and any of the hardeners known to the art may beused. Epoxy resins, for example, are commonly cured by primary-secondaryaliphatic amines such as diethylenetriamine, triethylenetetramine ortetraethylenepentamine; by ethylene oxide or propylene oxide adducts ofthe above such as N-(hydroxyethyl) diethylenetriamine or N,N'-bis(hydroxyethyl) -diethylenetriamine; by cyanoethylated primary-secondaryaliphatic amines; by primary-tertiary aliphatic amines such asdiethylaminopropylamine or dimethylaminopropylamine; by aromatic aminessuch as m-xylylenediamine; by liquid epoxy/amine adducts; by secondaryamines such as piperidine; by polyamides of long chain fatty acids suchas those marketed by General Mills under the tradename Versamid; by longchain polyamines such as the C -C alkyl diamines marketed by Armour &Co. under the trade name Duomeen and by Ciba Products Company under thetrade name Lancast A; by various liquid thiokol polymers such as thosemarketed by Thiokol Chemical Company under the designations LP-Z, LP3and LP8; by phenolic tertiary amines such as dimethylaminomethylphenoland tri-(dimethylaminomethyl)-phenol; by mixtures of the above and bymany other hardeners or curing agents, catalysts or initiators which areknown to those skilled in the art.

Unsaturated polyesters are generally catalyzed by peroxy, azo or othercompounds capable of generating free radicals. Typical hardeners orcuring agents include benzoyl peroxide, methyl ethyl ketone peroxide,cyclohexanone peroxide and cumene hydroperoxide. Systems intended forroom temperature cure generally make use of a promoter or acceleratorsuch as cobalt naphthenate, triethanolamine, triisopropanolamine,dimethyl phenylphosphine, stannous chloride or other multivalent metalsalts in the lower oxidation state, alkali metal sulfonates and otherswell known to the art. All of these are useful in the present inventionand may be used therein.

Polyurethane resin systems may be hardened or cured by Water; by variouspolyols such as butynediol, triethylene glycol, dimethyl propyleneglycol, glycerol monophenyl ether and their mixtures; by amines such asdimethylethanolamine, methyl morpholine andmethylenebis-(o-chloroaniline); b titanate esters; and by various othercross-linking agents which will be apparent to those skilled in the art.

It is well known that the addition of various other components to theseseveral resin systems will advantageously modify their properties inspecific directions, and such modifications may readily be incorporatedinto the prescut invention. For example, the addition of smallquantities of bisphenol-A will substantially shorten the cure time ofepoxy resins. Up to about -20% of nonreacting flexibilizers such as pineoil will increase the flexibility of cured epoxy systems. Variousorganic and inorganic compounds of chlorine, bromine or phosphorusimpart fire resistance. Many other additives, extenders, colorants,stabilizers, etc. are well known to the art.

The addition of surfactants to the present radiation and acousticbarriers is of particular advantage. Surfactants facilitate thedispersion of the thixotrope, prevent agglomeration of the thixotrope orthe powdered radiation attenuator during storage and permit adjustmentof the surface tension of the final composition to a value which isoptimum for either troweling or spraying. When a surfactant is used itmay be of virtually any kind, ionic or nonionic. Suitable surfactantsinclude the alkyl ethers of polyethylene glycol, ethoxylated octyl ornonyl phenol, polyoxyethylene sorbitan monolaurate, polyoxyethylenestearate, polyoxyethylene lauryl alcohol, sodium heptadecyl sulfate,sodium di-(2-ethylhexyl) phosphate, sodium tetradecyl sulfate; sodium2-ethylhexyl sulfate, various polydimethylsiloxanes, etc.

According to the present invention, the hardenable or thermoset resin,thixotropic agent and, if used, surfactant are mixed in varyingproportions depending on their nature and the intended use in a highshear mixer. The mixture so produced is then further combined with thepowdered radiation attenuator and the hardener or curing agent in asigma 01' blade-type mixer whereupon it may be directly applied to wallsand other vertical substratem without danger of sagging or running.

Further details of the invention are given in the following examples,which illustrate specific compositions and methods of making same butare not to be considered as limiting. On the contrary, persons skilledin the resin compounding art should be able to develop other variationsand modifications of this invention without departing from its spirit orfrom the scope of the appended claims.

Example 1 Parts Epon 815 (Shell Chemical Co. epoxy resin) 100 Cab-O-SilM5 (Cabot Corporation colloidal silica) 6.5 Glycerol 1.6Triethylenetetramine 12.5 Lead powder, 200 mesh 1230 The epoxy resin andCab-O-Sil were mixed with a mechanical stirrer until a homogeneousmixture was obtained. This was then further subjected to high shearmixing in a Cowles Dissolver for ten minutes. The glycerol was thenadded and high shear mixing was continued for another few minutes toachieve a uniform mass. The resultant composition was transferred to asigma-blade mixer where it was combined with the lead powder andtriethylenetetramine. The plastic barrier composition so produced issuitable for troweling onto vertical substrates without sagging orrunning. I

The radiation attenuating properties of the above composition werecompared with those of lead sheet by using the 662 kev. gamma rays fromCs and a Victoreen r meter. 0.264 inch of the above composition werefound to be equivalent to 0.159 inch of lead. Accordingly, on athickness basis, the above composition is 60% as effective as lead.

Example 2 Parts Araldite 507 (Ciba epoxy resin) 100 Cab-O-Sil EH5 (CabotCorp. colloidal silica) 7.7 Glycerol 2.0 Diethylenetriamine 11.0 Leadpowder, 325 mesh 985 The composition was mixed in the same manner asthat of Example 1 and provides a plastic shielding composition suitablefor spray application onto vertical surfaces of various types withoutsagging or running.

Example 3 Parts Araldite 507 (Ciba epoxy resin) Cab-O-Sil M-5 (CabotCorp. colloidal silica) 8.0 Glycerol 2.0 Versamid (General Millspolyamide) 35 Lead powder, 200 mesh 1450 Six parts of colloidal silicawere mixed with 100 parts of epoxy resin and dispersed under high shearconditions for ten minutes. 1.5 parts of glycerol were added to thismixture and high shear mixing was continued for another minute. Theremaining colloidal silica, i.e. 2.0 parts, was similarly dispersedunder high shear conditions in 35 parts of Versamid 125, which mixturewas then reinforced with the remaining 05 part of glycerol. The twoviscous resin mixtures were then combined with the powdered lead in ablade-type mixer and troweled onto the intended substrate. The productcures to a semi-flexible radiation and acoustic barrier which isparticularly useful under conditions where the substrata may not beentirely stable dimensionally or where such barriers must maintain longterm flexibility.

Example 4 The formulation of Example 3 was repeated except that 50 partsof Lancast A (Ciba Products Company) were used instead of 35 parts ofVersamid 125. The colloidal silica and glycerol were again dividedbetween the resin and the hardener, two thirds of each being mixed underhigh shear into the former, and one third into the latter. The productagain is a flexible radiation and acoustic barrier which is able tocontinuously adapt itself to dimensionally unstable substratas such aswood.

Example 5a Parts Araldite 506 (Ciba epoxy resin) 100 Thixcin R (BakerCastor Oil Co. hydrogenated castor oil) 12.5 Dow Corning 201(Polydimethylsiloxane) 0.5 Triethylenetetramine 12.5 Lead powder, 325mesh 1250 A mixture of the epoxy resin and the silicone surfactant washeated to 120130 F. at which point the Thixcin R was stirred in. Theresultant mixture was subjected to high shear mixing action at 120-130"F. for 15 minutes after which it was further mixed with the lead powderand curing agent in a blade-type mixer. The resultant formulation isvery satisfactory for trowel application to vertical surfaces.

Example 5b The formulation of Example 5a was repeated except that thethixotrope was omitted. The resultant composition was troweled to athickness of inch onto a wall seven feet high. By the time cure wasachieved 82% of the applied composition has drained to the floor.

Example 6 The formulation of Example 5a was repeated except that 15.0parts of Thixatrol ST (Baker Castor Oil Co. hydrogenated castor oil)were substituted for Thixcin R and 2050 parts of 300 mesh Wolfram powderwere substituted for lead powder. Dispersion of Thixatrol ST wasaccomplished under high shear conditions at F. The resultant barriercomposition can be applied directly to walls and on a thickness basis isapproximately as efl'ective as lead sheet.

7 Example 7 Parts Laminac 4110 (Cyanamid Chem. Co. polyester resin) 100Cab-O-Sil M (Cabot Corp. colloidal silica) 7.5 Ucon LB1717 (UnionCarbide surfactant) 1.0 Methyl ethyl ketone peroxide 0.5 Cobaltnaphthenate 0.1

Lead powder, 200 mesh 1100 The colloidal silica was dispersed in amixture of the polyester resin and the surfactant with high shearequipment for minutes. The mixture so produced was introduced to ablade-type mixer and further mixed with methyl ethyl ketone peroxide andcobalt naphenate. When a smooth mixture was obtained the lead powder wasadded and mixing was continued until complete dispersion had beenattained. The resultant plastic radiation and acoustic barriercomposition is suitable for both trowel or spray application to verticalsurfaces without sagging or running.

It is understood that the above examples are for illustrative purposesonly and that modifications may be made without departing from theinventive concept of the present invention and that I intend the scopeof the present invention to be set forth by the hereunto appendedclaims.

Having thus described my invention what I claim as new and desire toobtain by Letters Patent is:

1. A wall to be used for Shielding against penetrating radiation andnoise comprising a thermoset resin, a powdered radiation attenuatorselected from the group consisting of metals of high atomic number andhigh density and compounds, salts, mixtures, and alloys of said metals,and a thixotropic agent.

2. The wall of claim 1 wherein the thermoset resin is present in saidcomposition in an amount of about 1.5% to 25% by weight, the powderedradiation attenuator is present in said composition in an amount ofabout 75 to 98% by weight, and the thixotropic agent is present in saidcomposition in an amount of about 0.2% to 7.5% by weight.

3. The wall of claim 1 wherein the thixotropic agent is a memberselected from the group consisting of colloidal silica, hydrogenatedcastor oil, carboxy vinyl polymer, bentonite, kaolinite clay, colloidalcellulose and colloidal asbestos.

4. The wall of claim 1 wherein the thixotropic agent is present in saidcomposition in an amount of about 0.2 to 7.5% by weight of thecomposition.

5. The wall of claim 1 wherein the thermoset resin is a resin selectedfrom the group consisting of an epoxy resin, an unsaturated polyesterresin and a polyurethane resin.

6. The wall of claim 1 wherein said composition has incorporated thereina minor amount of surfactant.

7. A plastic radiation and acoustic barrier composition of matter havinga viscosity enabling it to 'be applied without sagging on verticalsurfaces comprising a thermoset resin, a powdered radiation attenuatorselected from the group consisting of metals of high atomic number andhigh density and compounds, salts, mixtures, and alloys of said metals,and a thixotropic agent.

8. The composition of claim 7 wherein the thermoset resin is present inan amount of about 1.5% to 25% by weight, the powdered radiationattenuator is present in an amount of about to 98% by weight, and thethixotropic agent is present in an amount of about 0.2% to 7.5% byweight.

9. The composition of matter of claim 7 wherein the thermoset resin is aresin selected from the group consisting of an epoxy resin, anunsaturated polyester resin, and a polyurethane resin.

10. The composition of matter of claim 7 wherein the radiationattenuator is a member selected from the group consisting of lead,Wolfram, bismuth, tantalum and ferrophosphorus.

11. The composition of matter of claim 7 wherein the thixotropic agentis selected from the group consisting of colloidal silica, hydrogenatedcastor oil, carboxy vinyl polymer, bentonite, kaolinite clay, colloidalcellulose and colloidal asbestos.

12. The composition of matter of claim 7 further containing a minoramount of surfactant.

13. A block to be used for shielding against penetrating radiation andnoise comprising a thermoset resin, a powdered radiation attenuatorselected from the group consisting of metals of high atomic number andhigh density and compounds, salts, mixtures, and alloys of said metals,and a thixotropic agent.

14. The block of claim 13 wherein the thermoset resin is present in saidcomposition in an amount of about 1.5 to 25 by weight, the powderedradiation attenuator is present in said composition in an amount ofabout 75% to 98% by weight, and the thixotropic agent is present in saidcomposition in an amount of about 0.2% to 7.5% by weight.

15. The block of claim 13 wherein the thixotropic agent is a memberselected from the group consisting of colloidal silica, hydrogenatedcastor oil, carboxy vinyl polymer, bentonite, kaolinite clay, colloidalcellulose and colloidal asbestos.

16. The block of claim 13 wherein the thermoset resin is a resinselected from the group consisting of an epoxy resin, an unsaturatedpolyester resin and a polyurethane resin.

17. The block of claim 13 wherein the radiation attenuator is a memberselected from the group consisting of lead, Wolfram, bismuth, tantalum,and ferrophosphorus.

18. The block of claim 13 wherein said composition has incorporatedtherein a minor amount of surfactant.

References Cited UNITED STATES PATENTS 3,200,085 8/1965 Guglielmo252-473 3,230,375 1/1966 Van Wagoner et al. 252-478 X 3,247,130 4/1966Isbell 252478 CARL D. QUARFORTH, Primary Examiner.

S. J. LECHERT, Assistant Examiner.

